Pi User Manual

Hai Fang1*, The ULTRA-DD Consortium2 and Julian C Knight1

1Wellcome Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
2https://ultra-dd.org

*hfang@well.ox.ac.uk

Abstract

Instructions on how to use an R/Bioconductor package “Pi”, a genetics-led system for the discovery and prioritisation of drug targets at the gene and pathway level. Taking as inputs disease-associated SNPs and their significance level (GWAS summary data) for specific immune traits, Pi uses genomic predictors to identify and score the likely modulated genes (termed seed genes) responsible for these genetic associations, on the basis of (i) genomic proximity of a gene to a trait-associated SNP (nGene); (ii) physical interaction between disease-associated SNPs and specific gene promoters evidenced by chromatin conformation (cGene) for primary immune cells; and (iii) modulation of gene expression (eGene) using expression quantitative trait loci (eQTL) mapped for major immune cell types in resting and activated states. Pi additionally uses annotation predictors comprising evidence for a gene with an immune function (fGene); immune phenotype (pGene); and rare genetic diseases related to immunity or the immune system (dGene). Pi also incorporates knowledge of gene interactions to iteratively explore network information and estimate connectivity (affinity scores) of a given gene product (network node) to a set of scored seed genes/nodes, identifying non-seed genes that lack genetic evidence but are highly ranked on the basis of network connectivity with prioritised seed genes. As such, a gene-predictor matrix that combines genomic and annotation predictors with knowledge of affinity scores is constructed from GWAS summary data. The prioritisation of target genes is enabled through meta-analysis (discovery mode) to prioritise target genes with substantial genetic support and/or with rich network connectivity. The prioritisation of target pathways individually and at crosstalk is based on the prioritised target genes.

Package

Pi 1.7.3

1 Package Citation

Hai Fang, The ULTRA-DD Consortium, Julian C Knight. Pi: an R/Bioconductor package leveraging genetic evidence to prioritize drug targets at the gene and pathway level. Bioconductor (2018); doi:10.18129/B9.bioc.Pi

2 Package Installation

2.1 R

See https://www.r-project.org or http://bioconductor.org/install/#install-R

2.2 Packages

# stable release version from Bioconductor
source("http://bioconductor.org/biocLite.R")
biocLite("Pi")

# development version from github
source("http://bioconductor.org/biocLite.R")
biocLite("devtools")
devtools::install_github("hfang-bristol/Pi")

3 Bug Reports

We are grateful to have your feedbacks particularly bug reports. Please file issues here for any bugs or other technical matters.

4 Pipeline Overview

Figure 1: Pi pipeline
Seed genes defined from input GWAS summary data using scores for genomic predictors to determine a gene (denoted by circle) being functionally linked to the input disease associated genetic variant (denoted by triangle) based on proximity, conformation and expression, each represented as different pie segments; scores for annotation predictors (immune function/phenotype/disease) then only applied to such seed genes. Knowledge of network connectivity defines non-seed genes, with an example showing how network connectivity with highly prioritised seed genes can identify a non-seed gene (TNF) in rheumatoid arthritis. Predictor matrix generates numerical Pi prioritisation rating (scored 0-5) and ranking (on genome-wide).

5 Core Functions

Figure 2: Pi functions
Designed in a nested way following this route: xPierSNPsAdv -> xPierSNPs -> xPierGenes -> xPier -> xRWR to prepare a gene-predict matrix and prioritisation of targe genes (xPierMatrix) taking as inputs disease-associated SNPs and their significance level (GWAS summary data) for specific traits. The output of this route is further taken as inputs for target pathway prioritisation (xPierPathways) or pathway crosstalk identification (xPierSubnet)

6 Getting started

Using curated GWAS summary data for rheumatoid arthritis (RA) as inputs, this section gives a step-by-step demo showing how to use Pi to achieve disease-specific prioritisation of drug targets at the gene and pathway level

First of all, load the package and specify the location of built-in data.

library(Pi)
RData.location <- "http://pi.well.ox.ac.uk/bigdata"

6.1 Input data

GWAS summary data for RA are primarily sourced from GWAS Catalog and ImmunoBase.

data.file <- "http://pi.well.ox.ac.uk/bigdata/GWAS_summary_data.RA.txt"
data <- read.delim(data.file, header=TRUE, stringsAsFactors=FALSE)

Table 1: The first 5 rows of data, with the column SNP for GWAS SNPs and the column pvalue for GWAS p-values

SNP	pvalue
rs998731	7.0e-09
rs9979383	5.0e-10
rs9826828	8.6e-10
rs968567	1.8e-08
rs9653442	1.6e-18

6.2 Prioritisation of target genes

Parameters used

include.LD <- 'EUR'
LD.r2 <- 0.8
LD.customised <- NULL
significance.threshold <- 5e-8
score.cap <- 10
distance.max <- 20000
decay.kernel <- "constant"
decay.exponent <- 2
eQTL.customised <- NULL
GR.SNP <- "dbSNP_GWAS"
#GR.SNP <- xRDataLoader('dbSNP_GWAS', RData.location=RData.location) # equivalent to this
GR.Gene <- "UCSC_knownGene"
#GR.Gene <- xRDataLoader('UCSC_knownGene', RData.location=RData.location) # equivalent to this
include.TAD <- "GM12878" # lymphoblast, reflective of immune-context genomic organisation
include.eQTL <- c("JKscience_CD14","JKscience_LPS2","JKscience_LPS24","JKscience_IFN","JKng_bcell","JKpg_CD4","JKpg_CD8","JKnc_neutro", "JK_nk", "WESTRAng_blood")
eQTL.customised <- NULL
include.HiC <- c("Monocytes","Macrophages_M0","Macrophages_M1","Macrophages_M2","Neutrophils","Naive_CD4_T_cells","Total_CD4_T_cells","Naive_CD8_T_cells","Total_CD8_T_cells","Naive_B_cells","Total_B_cells")
cdf.function <- "empirical"
scoring.scheme <- 'max'
network <- "STRING_high"
STRING.only <- NA
weighted <- FALSE
network.customised <- NULL
#network.customised <- xDefineNet("STRING_high", RData.location=RData.location)  # equivalent to this
seeds.inclusive <- TRUE
normalise <- "laplacian"
restart <- 0.7
normalise.affinity.matrix <- "none"
parallel <- TRUE
multicores <- NULL
verbose <- TRUE

Table 2: Explanation of eQTL (eGene) datasets used

Code	Name
JKscience_CD14	CD14+ (monocytes)
JKscience_LPS2	CD14+ by LPS2h
JKscience_LPS24	CD14+ by LPS24h
JKscience_IFN	CD14+ by IFN24h
JKng_bcell	B cells
JKpg_CD4	CD4+ T cells
JKpg_CD8	CD8+ T cells
JKnc_neutro	neutrophils
JK_nk	NK cells
WESTRAng_blood	peripheral blood

Table 3: Explanation of promoter capture Hi-C (cGene) datasets used

Code	Name
Monocytes	monocytes
Macrophages_M0	macrophages (M0)
Macrophages_M1	macrophages (M1)
Macrophages_M2	macrophages (M2)
Neutrophils	neutrophils
Naive_CD4_T_cells	CD4+ T cells (naïve)
Total_CD4_T_cells	CD4+ T cells (total)
Naive_CD8_T_cells	CD8+ T cells (naïve)
Total_CD8_T_cells	CD8+ T cells (total)
Naive_B_cells	B cells (naïve)
Total_B_cells	B cells (total)

Prioritisation

# prepare predictors
## first, genomic predictors
ls_pNode_genomic <- xPierSNPsAdv(data, include.LD=include.LD, LD.customised=LD.customised, LD.r2=LD.r2, significance.threshold=significance.threshold, score.cap=score.cap, distance.max=distance.max, decay.kernel=decay.kernel, decay.exponent=decay.exponent, GR.SNP=GR.SNP, GR.Gene=GR.Gene, include.TAD=include.TAD, include.eQTL=include.eQTL, eQTL.customised=eQTL.customised, include.HiC=include.HiC, cdf.function=cdf.function, scoring.scheme=scoring.scheme, network=network, STRING.only=STRING.only, weighted=weighted, network.customised=network.customised, seeds.inclusive=seeds.inclusive, normalise=normalise, restart=restart, normalise.affinity.matrix=normalise.affinity.matrix, parallel=parallel, multicores=multicores, verbose=verbose, RData.location=RData.location)
## then, annotation predictors
data.file <- file.path(RData.location, "iAnno.txt")
iAnno <- read.delim(data.file, header=TRUE, stringsAsFactors=FALSE)
iA <- iAnno[, 1:14]
ls_pNode_anno <- lapply(9:11, function(j){
    data_anno <- data.frame(seed=iA$Symbol, weight=iA[,j], stringsAsFactors=F)
    data_anno <- subset(data_anno, weight>0)
    pNode <- xPierAnno(data_anno, list_pNode=ls_pNode_genomic, network=network, STRING.only=STRING.only, weighted=weighted, network.customised=network.customised, seeds.inclusive=seeds.inclusive, normalise=normalise, restart=restart, normalise.affinity.matrix=normalise.affinity.matrix, parallel=parallel, multicores=multicores, verbose=verbose, RData.location=RData.location)
})
names(ls_pNode_anno) <- paste("Annotation_", colnames(iA)[9:11], sep='')
## bring together both predictors
ls_pNode <- c(ls_pNode_anno, ls_pNode_genomic)

# predictor matrix
df_predictor <- xPierMatrix(ls_pNode, displayBy="score", combineBy="union", aggregateBy="none", RData.location=RData.location)

# Prioritisation in a discovery mode
dTarget <- xPierMatrix(ls_pNode, displayBy="pvalue", combineBy="union", aggregateBy="fishers", RData.location=RData.location)   

The results are stored in an object called dTarget, a list with components including a data frame priority.

dTarget
## An object of S3 class 'dTarget', with 3 components:
##   $metag: an igraph object with 15430 nodes and 313918 edges
##   $predictor: a data frame of 15430 rows X 25 columns
##   $priority: a data frame of 15430 rows X 13 columns
## 
## --------------------------------------------------
## $priority:
##      name rank       pvalue          fdr priority
##  HLA-DRB1    1 2.715127e-43 4.189441e-39 5.000000
##  HLA-DQA1    2 2.003228e-41 1.545490e-37 4.889061
##                                             description Overall OMIM
##   major histocompatibility complex, class II, DR beta 1       4    1
##  major histocompatibility complex, class II, DQ alpha 1       5    1
##  Phenotype Function nearbyGenes eQTL HiC
##          0        0           1    6   7
##          1        1           1    0   9
## ......

The data frame dTarget$priority can be written into a text file Pi_output_priority.txt:

write.table(dTarget$priority, file="Pi_output_priority.txt", sep="\t", row.names=FALSE)

Manhattan plot

gp_manhattan <- xPierManhattan(dTarget, color='ggplot2', top=30, top.label.type="text", top.label.size=3, top.label.col="black", y.scale="normal", y.lab="Pi rating", RData.location=RData.location)
gp_manhattan

Figure 3: Manhattan plot
Priority scores (Pi rating) for genes are displayed on the Y-axis and genomic locations on the X-axis, with top 30 genes named

6.3 Prioritisation of target pathways

Pathway-level prioritisation is based on enrichment analysis of top 1% prioritised genes (top 150 genes) using a compendium of pathways (sourced from KEGG and REACTOME).

6.3.1 KEGG pathways

priority.top <- 150
eTerm1 <- xPierPathways(dTarget, priority.top=priority.top, ontology="KEGGorganismal", size.range=c(10,5000), test="fisher", min.overlap=10, RData.location=RData.location)
eTerm2 <- xPierPathways(dTarget, priority.top=priority.top, ontology="KEGGenvironmental", size.range=c(10,5000), test="fisher", min.overlap=10, RData.location=RData.location)
list_eTerm <- list(eTerm1, eTerm2)
names(list_eTerm) <- c('Organismal systems','Environmental information processing')
gp_kegg <- xEnrichCompare(list_eTerm, displayBy="zscore", FDR.cutoff=0.01, facet=F, signature=F)
gp_kegg

Figure 4: Barplot of prioritised KEGG pathways

6.3.2 REACTOME pathways

priority.top <- 150
eTerm <- xPierPathways(dTarget, priority.top=priority.top, ontology="REACTOME", size.range=c(10,5000), test="fisher", min.overlap=10, RData.location=RData.location)
gp_reactome <- xEnrichForest(eTerm, top_num=10, FDR.cutoff=0.01, CI.one=F, zlim=c(0,30), colormap="ggplot2.top", wrap.width=50, signature=F)
gp_reactome

Figure 5: Forest plot of prioritised REACTOME pathways

6.4 Identification of pathway crosstalk

An algorithm is developed to search for a subset of a gene network (merged from KEGG pathways) in a way that the resulting gene subnetwork (or crosstalk between different pathways) contains highly prioritized genes with a few less prioritized genes as linkers.

# obtain a gene network merged from KEGG pathways
networks <- c("KEGG_environmental","KEGG_organismal")
ls_ig <- lapply(networks, function(network){
    g <- xDefineNet(network=network, weighted=FALSE, verbose=FALSE, RData.location=RData.location)
})
ig <- xCombineNet(ls_ig, combineBy='union', attrBy="intersect", verbose=TRUE)

# search for a subset (with a desired node number of ~30) of the gene network 
g <- xPierSubnet(dTarget, network.customised=ig, priority.quantile=0.1, subnet.size=30, RData.location=RData.location)

# visualise pathway crosstalk with nodes colored by priority rating and labelled with evidence (seed genes)
gp_rating_evidence <- xVisEvidenceAdv(dTarget, nodes=V(g)$name, g=g, colormap="jet.top")
gp_rating_evidence

Figure 6: Visualisation of pathway crosstalk
Nodes/genes colored by priority rating and labelled with evidence (seed genes; colored segments)

7 Session Info

Here is the output of sessionInfo() on the system on which this user manual was compiled:

## R version 3.4.3 (2017-11-30)
## Platform: x86_64-apple-darwin15.6.0 (64-bit)
## Running under: OS X El Capitan 10.11.6
## 
## Matrix products: default
## BLAS: /Library/Frameworks/R.framework/Versions/3.4/Resources/lib/libRblas.0.dylib
## LAPACK: /Library/Frameworks/R.framework/Versions/3.4/Resources/lib/libRlapack.dylib
## 
## locale:
## [1] en_GB.UTF-8/en_GB.UTF-8/en_GB.UTF-8/C/en_GB.UTF-8/en_GB.UTF-8
## 
## attached base packages:
## [1] grid      stats     graphics  grDevices utils     datasets  methods  
## [8] base     
## 
## other attached packages:
##  [1] bindrcpp_0.2    png_0.1-7       BiocStyle_2.7.8 Pi_1.7.3       
##  [5] XGR_1.1.4       ggplot2_2.2.1   dnet_1.1.4      supraHex_1.13.3
##  [9] hexbin_1.27.1   igraph_1.1.2   
## 
## loaded via a namespace (and not attached):
##   [1] tidyselect_0.2.3              RSQLite_2.0                  
##   [3] AnnotationDbi_1.40.0          htmlwidgets_0.9              
##   [5] BiocParallel_1.12.0           munsell_0.4.3                
##   [7] units_0.4-6                   codetools_0.2-15             
##   [9] misc3d_0.8-4                  withr_2.1.0                  
##  [11] colorspace_1.3-2              BiocInstaller_1.28.0         
##  [13] Biobase_2.38.0                OrganismDbi_1.20.0           
##  [15] highr_0.6                     knitr_1.20                   
##  [17] rstudioapi_0.7                stats4_3.4.3                 
##  [19] ROCR_1.0-7                    robustbase_0.92-8            
##  [21] dimRed_0.1.0                  labeling_0.3                 
##  [23] GenomeInfoDbData_0.99.1       mnormt_1.5-5                 
##  [25] bit64_0.9-7                   rprojroot_1.2                
##  [27] xfun_0.1                      ipred_0.9-6                  
##  [29] biovizBase_1.26.0             randomForest_4.6-12          
##  [31] R6_2.2.2                      doParallel_1.0.11            
##  [33] GenomeInfoDb_1.14.0           AnnotationFilter_1.2.0       
##  [35] DRR_0.0.2                     bitops_1.0-6                 
##  [37] reshape_0.8.7                 DelayedArray_0.4.1           
##  [39] assertthat_0.2.0              scales_0.5.0                 
##  [41] nnet_7.3-12                   gtable_0.2.0                 
##  [43] ddalpha_1.3.1                 ggbio_1.26.1                 
##  [45] ensembldb_2.2.0               timeDate_3042.101            
##  [47] rlang_0.1.6                   CVST_0.2-1                   
##  [49] RcppRoll_0.2.2                splines_3.4.3                
##  [51] rtracklayer_1.38.1            lazyeval_0.2.1               
##  [53] ModelMetrics_1.1.0            acepack_1.4.1                
##  [55] dichromat_2.0-0               broom_0.4.3                  
##  [57] checkmate_1.8.5               intergraph_2.0-2             
##  [59] yaml_2.1.18                   reshape2_1.4.2               
##  [61] GenomicFeatures_1.30.0        ggnetwork_0.5.1              
##  [63] backports_1.1.1               httpuv_1.3.5                 
##  [65] Hmisc_4.0-3                   RMySQL_0.10.13               
##  [67] RBGL_1.54.0                   caret_6.0-77                 
##  [69] tools_3.4.3                   lava_1.5.1                   
##  [71] bookdown_0.7                  psych_1.7.8                  
##  [73] statnet.common_4.0.0          gplots_3.0.1                 
##  [75] RColorBrewer_1.1-2            BiocGenerics_0.24.0          
##  [77] Rcpp_0.12.15                  plyr_1.8.4                   
##  [79] base64enc_0.1-3               progress_1.1.2               
##  [81] zlibbioc_1.24.0               purrr_0.2.4                  
##  [83] RCurl_1.95-4.8                prettyunits_1.0.2            
##  [85] deldir_0.1-14                 rpart_4.1-11                 
##  [87] S4Vectors_0.16.0              sfsmisc_1.1-1                
##  [89] SummarizedExperiment_1.8.0    ggrepel_0.7.0                
##  [91] cluster_2.0.6                 magrittr_1.5                 
##  [93] data.table_1.10.4-3           sna_2.4                      
##  [95] ProtGenerics_1.10.0           matrixStats_0.52.2           
##  [97] evaluate_0.10.1               mime_0.5                     
##  [99] xtable_1.8-2                  XML_3.98-1.9                 
## [101] IRanges_2.12.0                gridExtra_2.3                
## [103] compiler_3.4.3                biomaRt_2.34.0               
## [105] tibble_1.4.2                  KernSmooth_2.23-15           
## [107] htmltools_0.3.6               Formula_1.2-2                
## [109] udunits2_0.13                 tidyr_0.7.2                  
## [111] lubridate_1.7.1               DBI_0.7                      
## [113] tweenr_0.1.5                  MASS_7.3-47                  
## [115] Matrix_1.2-12                 gdata_2.18.0                 
## [117] parallel_3.4.3                Gviz_1.22.1                  
## [119] bindr_0.1                     gower_0.1.2                  
## [121] GenomicRanges_1.30.0          pkgconfig_2.0.1              
## [123] GenomicAlignments_1.14.1      RCircos_1.2.0                
## [125] foreign_0.8-69                recipes_0.1.1                
## [127] foreach_1.4.3                 XVector_0.18.0               
## [129] prodlim_1.6.1                 stringr_1.3.0                
## [131] VariantAnnotation_1.24.2      digest_0.6.12                
## [133] graph_1.56.0                  Biostrings_2.46.0            
## [135] rmarkdown_1.9                 htmlTable_1.11.0             
## [137] curl_3.0                      kernlab_0.9-25               
## [139] shiny_1.0.5                   Rsamtools_1.30.0             
## [141] gtools_3.5.0                  nlme_3.1-131                 
## [143] network_1.13.0                BSgenome_1.46.0              
## [145] pillar_1.1.0                  lattice_0.20-35              
## [147] GGally_1.3.2                  httr_1.3.1                   
## [149] DEoptimR_1.0-8                survival_2.41-3              
## [151] interactiveDisplayBase_1.16.0 glue_1.2.0                   
## [153] iterators_1.0.8               plot3D_1.1.1                 
## [155] glmnet_2.0-13                 bit_1.1-12                   
## [157] Rgraphviz_2.22.0              ggforce_0.1.1                
## [159] class_7.3-14                  stringi_1.1.7                
## [161] blob_1.1.0                    AnnotationHub_2.10.1         
## [163] latticeExtra_0.6-28           caTools_1.17.1               
## [165] memoise_1.1.0                 dplyr_0.7.4                  
## [167] ape_5.0